title: Variation at the b Mating Type Locus of Ustilago maydis.
abstract: ABSTRACT Population level diversity at the Ustilago maydis b mating type locus was determined in samples from four Minnesota locations using a combination of plate mating techniques and a polymerase chain reaction (PCR)-based assay. The PCR method allows rapid identification of b types from samples of natural populations and utilizes the hypervariable regions of the b locus that determine mating type specificity. Results demonstrated high levels of b diversity within populations, with one population yielding 17 of the total 18 b types found in the study. Pairwise G(ST) values were in the range of 0.02 to 0.05, and common b mating types were found across broad geographic distances. These data demonstrated that very low levels of differentiation among U. maydis populations occur with respect to b locus variation. Consistent with frequency-dependent selection models, b types were represented at approximately equal frequencies within the entire Minnesota population. However, neutral evolutionary models for patterns of geographic distribution and variation at b cannot be entirely excluded. The importance to agricultural practices of understanding population genetic processes is discussed.
authors.forename: P
authors.initials: P
authors.lastname: Zambino
authors.forename: J V
authors.initials: JV
authors.lastname: Groth
authors.forename: L
authors.initials: L
authors.lastname: Lukens
authors.forename: J R
authors.initials: JR
authors.lastname: Garton
authors.forename: G
authors.initials: G
authors.lastname: May